Rails used in the construction of railroad track require heat treatment to withstand metallurgical failure in normal use. FIG. 1(a) and FIG. 1(b) illustrate a typical flat-bottom rail 90 comprising head 90a, web 90b and foot 90c. Heat treatment, or metallurgical hardening, is sometimes focused on the rail's head since the head is the region that makes contact with the wheels of rolling stock, while the web connects the head to the foot for distribution of the bearing load to sleepers, or ties, and the bed beneath the rails. FIG. 1(c) illustrates typical terminology that is used to describe approximate regions of the head. The crown, or running surface, is the region making contact with a wheel's rim, while the wheel's flanges generally make contact with one side surface of the head. Lower jaw regions define the region of the head that connects the head to web 90b. Modern railroad design, for example rails for high speed trains, can require relatively long lengths of a continuous rail, for example, in excess of 20 meters. Rails can be fabricated in a hot rolling mill that produces a hot length of rail by forging.
Heat treatment of the rail can be accomplished upon exit from the rolling mill, for example, by proper scaling of the rail and quenching with a fluid medium, such as air and/or water.
Satisfactory heat treatment of the rail's head must be performed when at least the cross sectional temperature profile of the head is generally the same along the entire longitudinal length, Lr, of the head. One approach is to heat the entire length of rail (that is, the head, web and foot) to the preferred cross sectional temperatures in the head, web and foot after hot rail fabrication to minimize deformation of the rail. Typically an axial (solenoidal) coil is used where the entire cross section of the rail passes through the axial coil to be inductively heated. FIG. 1(d) and FIG. 1(e) illustrate with diagrammatic arrows the direction of instantaneous current flow around a cross section of a rail passing through an axial coil. Axial induction heating coils are ideal when the workpiece passing through the axial coil has a generally shaped perimeter such as a metal strip or slab (rectangular shape) or tubular (circular shape) for excellent temperature uniformity. When the workpiece has a non-generally shaped (complex) perimeter such as the rail shown in FIG. 1(b) axial heating results in overheating of the foot (a shape with a high surface-to-volume ratio) and under heating of the head (a shape with a low surface-to-volume ratio compared to the foot). This differential temperature between the foot and head can create severe deformation of the rail due to the high heat expansion of the foot in comparison with the low heat expansion of the head. Consequently massive straightening rolls are required to keep the inductively heated rail from deforming as it passes through one or more axial induction coils.
Another approach is to preferably heat only the head of the rail to preferred cross sectional temperature after rail fabrication.
In either approach identified in the two previous paragraphs the different masses of the rail head, web and foot need to be considered relative to magnitude of applied induction power and “heat soaking” of the inducted heat into the rail head, web and foot.
One object of the present invention includes adjusting the temperature of the entire cross sectional temperature profile of a rail throughout the entire length of the rail with a transverse flux electric inductor rail heater.
Another object of the present invention includes adjusting the temperature of the cross section (transverse) profile of a rail's head throughout the entire length of the rail with an electric induction heater.
Another object of the present invention includes heating the entire cross sectional temperature profile of the opposing ends of two adjacent rail sections with a transverse flux electric inductor rail heater prior to welding together the two opposing ends of the rail sections.
Another object of the present invention is to induce more heating power into the head than in the foot of a rail with a transverse flux electric inductor to achieve the same temperature increase in the foot and head regions in order to avoid or minimize the deformation of the rail.